/* SPDX-License-Identifier: GPL-2.0-or-later *//* * Queue read/write lock * * These use generic atomic and locking routines, but depend on a fair spinlock * implementation in order to be fair themselves.  The implementation in * asm-generic/spinlock.h meets these requirements. * * (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P. * * Authors: Waiman Long <waiman.long@hp.com> */#ifndef __ASM_GENERIC_QRWLOCK_H#define __ASM_GENERIC_QRWLOCK_H #include <linux/atomic.h>#include <asm/barrier.h>#include <asm/processor.h> #include <asm-generic/qrwlock_types.h> /* Must be included from asm/spinlock.h after defining arch_spin_is_locked.  */ /* * Writer states & reader shift and bias. */#define	_QW_WAITING	0x100		/* A writer is waiting	   */#define	_QW_LOCKED	0x0ff		/* A writer holds the lock */#define	_QW_WMASK	0x1ff		/* Writer mask		   */#define	_QR_SHIFT	9		/* Reader count shift	   */#define _QR_BIAS	(1U << _QR_SHIFT) /* * External function declarations */extern void queued_read_lock_slowpath(struct qrwlock *lock);extern void queued_write_lock_slowpath(struct qrwlock *lock); /** * queued_read_trylock - try to acquire read lock of a queued rwlock * @lock : Pointer to queued rwlock structure * Return: 1 if lock acquired, 0 if failed */static inline int queued_read_trylock(struct qrwlock *lock){	int cnts; 	cnts = atomic_read(&lock->cnts);	if (likely(!(cnts & _QW_WMASK))) {		cnts = (u32)atomic_add_return_acquire(_QR_BIAS, &lock->cnts);		if (likely(!(cnts & _QW_WMASK)))			return 1;		atomic_sub(_QR_BIAS, &lock->cnts);	}	return 0;} /** * queued_write_trylock - try to acquire write lock of a queued rwlock * @lock : Pointer to queued rwlock structure * Return: 1 if lock acquired, 0 if failed */static inline int queued_write_trylock(struct qrwlock *lock){	int cnts; 	cnts = atomic_read(&lock->cnts);	if (unlikely(cnts))		return 0; 	return likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts,				_QW_LOCKED));}/** * queued_read_lock - acquire read lock of a queued rwlock * @lock: Pointer to queued rwlock structure */static inline void queued_read_lock(struct qrwlock *lock){	int cnts; 	cnts = atomic_add_return_acquire(_QR_BIAS, &lock->cnts);	if (likely(!(cnts & _QW_WMASK)))		return; 	/* The slowpath will decrement the reader count, if necessary. */	queued_read_lock_slowpath(lock);} /** * queued_write_lock - acquire write lock of a queued rwlock * @lock : Pointer to queued rwlock structure */static inline void queued_write_lock(struct qrwlock *lock){	int cnts = 0;	/* Optimize for the unfair lock case where the fair flag is 0. */	if (likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED)))		return; 	queued_write_lock_slowpath(lock);} /** * queued_read_unlock - release read lock of a queued rwlock * @lock : Pointer to queued rwlock structure */static inline void queued_read_unlock(struct qrwlock *lock){	/*	 * Atomically decrement the reader count	 */	(void)atomic_sub_return_release(_QR_BIAS, &lock->cnts);} /** * queued_write_unlock - release write lock of a queued rwlock * @lock : Pointer to queued rwlock structure */static inline void queued_write_unlock(struct qrwlock *lock){	smp_store_release(&lock->wlocked, 0);} /** * queued_rwlock_is_contended - check if the lock is contended * @lock : Pointer to queued rwlock structure * Return: 1 if lock contended, 0 otherwise */static inline int queued_rwlock_is_contended(struct qrwlock *lock){	return arch_spin_is_locked(&lock->wait_lock);} /* * Remapping rwlock architecture specific functions to the corresponding * queued rwlock functions. */#define arch_read_lock(l)		queued_read_lock(l)#define arch_write_lock(l)		queued_write_lock(l)#define arch_read_trylock(l)		queued_read_trylock(l)#define arch_write_trylock(l)		queued_write_trylock(l)#define arch_read_unlock(l)		queued_read_unlock(l)#define arch_write_unlock(l)		queued_write_unlock(l)#define arch_rwlock_is_contended(l)	queued_rwlock_is_contended(l) #endif /* __ASM_GENERIC_QRWLOCK_H */